Surf Science: The Basics Of EPS Foam

The Basics Of EPS Foam
It’s more than just a mysterious acronym.

Words: Casey Koteen
Photo:
John King

Know it or not, you might be familiar with EPS foam already. Ever checked out one of those disposable foam coolers at the grocery store? Yep, it’s a close version of EPS, which is gaining momentum as an alternative to traditional polyurethane foam—the material most surfboard blanks have been made out of since the mid 1950s. But don’t be scared, EPS is just a shorter way of saying expanded polystyrene. So beyond the name, what is EPS and how is it different than polyurethane foam?

On the rack and finished, besides being lighter, it’s nearly impossible to tell an EPS board apart from a polyurethane. But if you looked closely at the two different blanks, you’d notice the size of the EPS cells is bigger. Polyurethane foam looks like it’s made of small, almost sand-sized granules. Though EPS cell structure does come in a variety of sizes, the most common used for surfboards has a cell size of about 1/8”, similar in shape and size to a BB.

EPS is hand- and machine-shapeable, although because of the larger cell size, it’s not quite as easy to shape as polyurethane foam. The upside of it being accessible to those used to traditional shaping techniques is that it supports the custom-surfboard industry. “Regardless of the materials,” says Geoff Rashe of M10 Surfboards, “it’s got to be the right shape for the rider. So it’s still a custom business, and with EPS you’ve got that.”

Also, EPS blanks are glassed with epoxy resin. There are lots of misconceptions about epoxy resin, perhaps the most common that it’s automatically equated with Surftech, or a molded surfboard. “When you say epoxy, everyone thinks it’s all the same,” says Bill “Stretch” Riedel of Stretch surfboards, who’s been working with EPS, other styrene-based foams, and epoxy resins for twenty years. “Epoxy is just a resin, a glue. It has nothing to do with the makeup of the board.”

Riedel is a pioneer of using EPS for surfboards and says that many of the early problems with it have been worked out. One issue was that the blanks absorbed water easily, but that was fixed about two years ago. “As soon as that happened we went strongly back into epoxy,” he says. “Now we’re using what’s called two-pound fusion-grade EPS.”

That’s a quick look at the nuts and bolts of EPS, but what about how they ride? Stretch says the most immediately noticeable difference with an EPS board is that they feel more buoyant when paddling. Beyond that, the general consensus is that they surf very similarly to polyester boards.

Although lots of big-name shapers have been experimenting with EPS in recent months, only time will tell if it’ll gain mass acceptance. “I don’t know how long it’s going to take,” says Stretch, “but in my opinion, it will change the way surfboards are built.”

Originally published in the July, 2006 issue of Transworld SURF.